The invention is described in terms of a vehicle which inspects ductile iron gas distribution pipelines, the vehicle being towed through the pipeline by means of a flexible member, such as a cable, attached to a winch. However, the invention is applicable quite generally and includes vehicles for use in inspecting gas or oil transmission pipelines, or pipelines for conveying water or other liquids which in most cases are propelled through the pipeline by a pressure difference across the vehicle owing to the pressure difference applied to drive the fluid through the pipeline.
British patent specification No. GB-B-1535252 describes a pipeline inspection vehicle for inspecting gas transmission lines. The vehicle has an array of sensor mountings arranged around the body of the vehicle. Each sensor is mounted on a metal plate or sledge adapted to run along the inside surface of the pipeline to be inspected. The leading end of the plate is connected by a flexible member to an anchorage on the vehicle. A metal spring also mounted on an anchorage on the vehicle has two spring arms, the first of which bears against the flexible member and the second of which bears against the trailing end of the plate.
Thus, the plate is urged towards the pipeline by spring forces applied at its ends.